The formation of SiO.sub.2 layers that fill high aspect ratio gaps (e.g., vertical shallow trenches, contacts, vias, etc.) without voids and are capable of a high degree of planarity is becoming extremely important in advanced dynamic random access memory devices (DRAMS). This is because the geometries are getting very small and high integrity interlayer dielectrics are needed.
Conventional methods of depositing SiO.sub.2 involve low pressure, and even subatmospheric, chemical vapor deposition as well as plasma-enhanced chemical vapor deposition to avoid the appearance of voids. These methods, however, are not completely successful. That is, voids can still form, particularly in vertical trenches.
Gaillard et al., J. Vac. Sci. Technol. B, 14, 2767-2769 (1996) describe an improved method that involves the formation of a liquid to completely fill high aspect ratio gaps with a homogeneous SiO.sub.2 layer. This method forms liquid Si(OH).sub.x (O).sub.y (H.sub.2 O).sub.z from the gas phase using chemical vapor deposition (CVD) of a mixture of SiH.sub.4, H.sub.2 O, and H.sub.2 O.sub.2. The liquid material forms a planar surface by surface tension. It then polymerizes to hydrated silica and is further densified to amorphous SiO.sub.2 by annealing. This is referred to as a SiO.sub.2 "FLOWFILL" method. However, this method is not as versatile as is desired with respect to etch rate and/or selectivity with respect to other oxide or nitride layers.
Thus, there is a continuing need for methods that provide layers on surfaces having small high aspect ratio openings that have few, if any, voids and have different and/or improved planarization and etch characteristics relative to conventionally formed SiO.sub.2 layers, particularly in advanced dynamic random access memory devices.